Coaxial cables are widely used in the industry to distribute signals. Such cables include a central inner conductor surrounded by a low loss, high dielectric foam. The foam dielectric is, in turn, surrounded by a metallic outer conductor which may be cylindrical or corrugated. A protective insulating jacket, or sheath, surrounds the metallic outer conductor. The ends of such coaxial cables must be connected to junction boxes, amplifiers, and other coaxial ports, and coaxial connectors are well known for terminating the ends of coaxial cables. One example of such a coaxial cable connector is disclosed in U.S. Pat. No. 6,183,298 to Henningsen. The connector disclosed in the Henningsen '298 patent includes a main body, a bushing or back nut, a center conductor, and an insulator supporting the center conductor within the main body.
When designing such connectors for manufacture, one of the principal design goals is to minimize the possibility that water or moisture will migrate through the connector from the external environment and degrade the mechanical and/or electrical characteristics of the connector. Degradation of the electrical characteristics of the connector can have a detrimental impact upon the ability of a cable system operator to provide reliable signal transmission.
In order to maintain a desired characteristic impedance within the coaxial cable, manufacturers of coaxial cable tightly control the diameters of the inner conductor, the outer conductor, and the dielectric material that lies between such conductors. On the other hand, since the outer jacket of the cable does not affect the transmission characteristics of the coaxial cable, manufacturing tolerances of such protective outer jackets are not held to the same standards. Nonetheless, one of the points at which water or moisture can be introduced into such a coaxial connector is at the junction between the coaxial cable outer protective jacket and the back nut of the connector. The most common practice used by manufacturers of coaxial connectors to prevent moisture migration at the interface between the back nut and the cable jacket is to install a sealing within the back nut for being compressed between the inner bore of the back nut and the cable jacket.
The use of sealing in the manner explained above does not truly solve the problem of moisture migration over time. While a given coaxial connector may be designed for use with a number of different brands of coaxial cable, the variance in cable jacket outer diameter dimensions from brand to brand (and sometimes within the same brand), sealing are compressed to a greater or lesser extent. When the pressure exerted on the O-ring (e.g.) varies widely, its ability to seal the interface can be jeopardized. Ideally, an O-ring should only be pressurized to about 10-20% of thickness. However, in order to maintain O-ring pressurization within such range, variations in the outer diameter of the cable jacket would need to be held to 0.30-0.50 mm. In contrast, the dimensions of the outer diameter of the cable jacket often vary between 1 to 2 mm.
Moreover, even if the thickness of the cable jacket were more rigorously controlled, leakage paths can still develop due to irregularities introduced into the outer surface of the cable jacket. For example, such irregularities can be cause by the corrugations in the outer conductor, which effectively form grooves in the cable jacket. Alternatively, valleys, nicks, scratches and grooves can be introduced into the outer surface of the cable jacket during transport and/or installation, as by contact with rocks or stones as the coaxial cable is pulled from its supply reel. Such imperfections can also cause the sealing within the back nut to fail.
Accordingly, it is an object of the present invention is to provide a simple, yet effective method of reliably sealing the back nut of a coaxial cable connector over the cable jacket.
A further object of the invention is to provide such a method that would allow a given coaxial cable connector to work reliably with a larger number of types of coaxial cable without risking moisture migration failure at the interface between the back nut and the cable jacket.
A still further object of the present invention is to provide such a method that would allow a given coaxial cable connector to adapt itself to a relatively wide variation in the outer diameter of coaxial cable jackets without risking moisture migration failure at the interface between the back nut and the cable jacket.
Another object of the present invention is to provide such a method which eliminates the deleterious effects of valleys, nicks, scratches and grooves that are introduced into the outer surface of the cable jacket during transport and/or installation.
Still another object of the present invention is to provide such a method which more reliably maintains the pressure on sealing within its optimal pressure range to better seal the interface between the back nut and cable jacket.
Yet another object of the present invention is to provide a coaxial cable preparation tool that facilitates the practice of the improved sealing method as outlined above.
These and other objects of the present invention will become more apparent to those skilled in the art as the description of the present invention proceeds.